Sink basin



FIG. 1 is a top view Of a design for a sink basin showing our new design; FIG. 2 is a top view of a second variant of the design for a sink basin shown in FIG. 1; and, FIG. 3 is a perspective view of a third variant of the design for a sink basin shown in FIG. 1. 

The ornamental design for a sink basin, as shown and described. 